Internal combustion engines, for example, diesel engines, gasoline engines, or natural gas engines employ turbochargers to deliver compressed air for combustion in the engine. A turbocharger compresses air flowing into the engine, helping to force more air into combustion chambers of the engine. The increased supply of air allows for increased fuel combustion in the combustion chambers of the engine, resulting in increased power output from the engine.
A typical turbocharger includes a housing, a shaft, a turbine wheel attached to one end of the shaft, a compressor wheel connected to the other end of the shaft, and bearings to support the shaft. Exhaust from the engine expands over the turbine wheel and rotates the turbine wheel. The turbine wheel in turn rotates the compressor wheel via the shaft. The compressor wheel receives cool air from the ambient and forces compressed air into combustion chambers of the engine.
An oil pump typically provides pressurized oil to lubricate the turbocharger bearings located within a bearing housing. The turbocharger shaft may also include features that may help to sling the oil away from the shaft through centrifugal forces generated during operation of the turbocharger. Slinging oil away from the shaft makes it harder for the oil to leak through gaps between the shaft and the bearing housing into the compressor volute. Seals between shaft and the bearing housing also help ensure that oil does not escape into the compressor volute. The seals also prevent excessive air leakage into the oil drain cavity of the turbocharger. Air leakage into the turbocharger can pressurize the attached engine crankcase and place additional demands on the crankcase ventilation system.
Although a simple seal geometry may minimize the manufacturing costs, a simplified geometry may also make the seal less effective. In particular, a simple seal geometry may not prevent oil from reaching the gap between the shaft and the surrounding housing when the turbocharger remains inoperative or when the turbocharger operates at reduced rotational speed, preventing the oil from being effectively flung away from the shaft. Thus, balancing manufacturing costs and sealing effectiveness becomes important when designing a seal for the compressor in a turbocharger.
One attempt to address some of the problems described above is disclosed in European Patent Application No. 2 615 261 A1 of Ramasamy et al. that published on Jul. 17, 2013 (“the '261 publication”). In particular, the '261 publication discloses a turbocharger shaft including a boss at the compressor end having a larger diameter compared to the shaft. The '261 publication further discloses that the boss is received in a bore of the compressor housing. The '261 publication also discloses that the outer surface of the boss has an annular groove, which receives a piston ring attached to the inner walls of the bore of the compressor housing. In addition, the '261 publication discloses that the boss includes an integrally formed oil slinger. The '261 publication also discloses that the area of the bearing housing that surrounds the oil slinger includes an annular chamber that captures the dispersed oil and allows oil to flow out of a drain.
Although the '261 publication discloses a compressor oil seal, the disclosed seal may still be less than optimal. In particular, the use of a piston ring, as disclosed in the '261 publication, requires a back stop to locate the piston ring and resist pressure loads generated by the gases behind the impeller. Further, due to the tight fit between the axial faces of the piston ring and the corresponding walls of the rotating annular groove, the back stop location must remain very tightly controlled axially and the turbocharger shaft must also attenuate axial free play to a small amount such that the groove doesn't excessively wear into the piston ring. The need for such tightly controlled dimensions increases the manufacturing cost. In addition, imbalance in the impeller or the shaft, during degraded states of operation, can overcome the radial clearance between the piston ring and groove, damaging both the piston ring and surrounding rotor and housing pieces. The oil slinger disclosed in the '261 publication may also be less than optimal for other reasons. In particular, a diameter of the oil slinger in the '261 publication appears to be only slightly larger than that of the shaft. Moreover, the oil dispersed by the slinger of the '261 publication is captured by the annular recess and drained to the sump. As a result the oil dispersed from the shaft may not be available to cool the bearing housing. The seal of the '261 publication may also be unable to prevent oil leakage when the turbocharger is not operational.
The compressor seal of the present disclosure solves one or more of the problems set forth above and/or other problems of the prior art.